Rather than having bindings use g_function_info_invoke, which is basically
a toy/demo API, export a convenience utility function which takes the introspection
information and sets up things we need to pass to libffi.
Then invocation can be done directly to libffi by a binding.
As part of this work, remove some (unused by gjs) public functions from the
girffi API, and instead export a function to map to libffi which can work
semi-correctly.
https://bugzilla.gnome.org/show_bug.cgi?id=604074
Extract a function to convert GITypeTag to ffi_type from the internals
of ginvoke.c. This will be useful in figure out structure alignment.
Also fix handling of gsize and time_t to be portable. (Add a check
to configure.ac to figure out the width of time_t.)
svn path=/trunk/; revision=873
